1. Field of the Invention
The present invention relates to papermaking machines, and, more particularly, to fabrics used in papermaking machines.
2. Description of the Related Art
In the manufacturing of tissue products, particularly absorbent tissue products, there is a continuing need to improve the physical properties of the tissue and offer a differentiated product appearance. It is generally known that molding a partially dewatered celluslosic web on a topographical papermaking fabric will enhance the finished paper product's physical properties. Such molding can be applied by fabrics in an uncreped through air dried process as disclosed in U.S. Pat. No. 5,672,248 to Wendt et al, or in wet pressed tissue manufacturing processes as disclosed in U.S. Pat. No. 4,637,859 to Trokhan, U.S. Pat. No. 4,849,054 to Klowak, U.S. Pat. No. 6,287,426 to Edwards et al., or US patent application US 2006/0090867 A1 by Herman et al.
Wet molding typically imparts desirable physical properties independent of whether the tissue is subsequently creped as disclosed in US patent application 2006/0090867 A1, or an uncreped tissue product is produced. Hence, it is generally desirable to continuously improve the papermaking fabric's topography for improved molding characteristics, tissue structure, and tissue crepability.
U.S. Pat. No. 4,161,195 to Khan refers to papermaking fabrics which are 5-shed or greater and woven in non-regular twill patterns such that the warp and shute yarns have an “evensided” amount of interlacings in each unit weave repeat and no knuckle exceeds more than three crossovers in length. Generally the MD and CD knuckles are coplanar in the top surface plane of the fabric, although this is not a requirement. The fabrics have relatively short warp floats passing over no more than three shutes and little overlap of the MD knuckles.
U.S. Pat. No. 5,832,962 to Kaufman and Herman describe warp dominant TAD fabrics containing a first axis of bulky ridges defined by long warp knuckles on adjacent threads oriented at 68 to 90 degrees from the CD and a second axis formed by the long warp knuckles with other overlapping long warp knuckles on nearby warp threads with an angle of less than 23 degress from the CD. The fabric ridges are no higher than the height of a single warp strand since they are based on adjacent warp yarns which overlap in the machine direction but not in the z-direction. The ridges are located on a bias with respect to the MD due to their overlapping construction. Example fabrics have at least 4 interlacings in a unit weave repeat, at least 3 breaks, lateral yarn crimp, and are 9-shed or greater.
U.S. Pat. No. 5,429,686 to Chiu et al. discloses a through air drying fabric with a distinct load-bearing woven fabric layer and an additional sculpture layer formed by additional long-floated machine direction yarns, with the floats standing proud of the main body of the load-bearing fabric layer to shape the formed sheet.
U.S. Pat. No. 4,239,065 describes fabrics having “wicker-basket-like cavities” staggered in both MD and CD. Co-planar top surface knuckles surround the cavities, which span sub-top-surface crossovers or knuckles. The pickets surrounding the cavities are imprinted into the sheet in a wet-pressed papermaking operating. U.S. Pat. Nos. 6,592,714 and 6,649,026 to Lamb describe larger cavities than Trokhan wherein the cavities contain warp and shute interlacings. The cavities are dimensioned by pocket depths measured between two planes internal to the fabric structure.
Additional fabrics are described in U.S. Pat. No. 5,228,482 to Fleischer which offer interconnected pockets instead of Trokhan's discrete cavities based on a top-surface plane of MD knuckles with a sub-top-surface plane of CD knuckles and a lower sup-top-surface plane of MD knuckles.
U.S. Pat. No. 6,237,644 B1 to Hay et al. describe fabrics having a continuous lattice separating woven areas with at least three yarns in MD and CD.
U.S. Pat. No. 6,998,024 B2 to Burazin et al. disclose papermaking fabrics with substantially continuous machine direction ridges whereby the ridges are made up of multiple warp strands grouped together. The ridges are higher and wider than individual warps. The wide wale ridges have a ridge width of about 0.3 cm or greater and the frequency of occurrence of the ridges in the CD is from about 0.2 to 3 per centimeter. In the examples shown, the shute diameters are both larger than or smaller than the warp diameters but only one shute diameter is utilized.
US patent application US 2005/0236122 A1 by Mullally et al. disclose woven papermaking fabrics which have deep, discontinuous pocket structures with a regular series of distinct, relatively large depressions in the fabric surface surrounded by raised warp or raised shute strands. The pockets could be of any shape, with their upper edges on the pocket sides being relatively even or uneven, but the lowest points of individual pockets are not connected to the lowest points of other pockets. The most common examples are all waffle-like in structure and could be warp dominant, shute dominant, or coplanar. The pocket depths can be from about 250 to about 525 percent of the warp strand diameter.
Additional patents cover materials adhered to the surface of either a flat or topographical fabric such as the application of a resinous framework or polymer pattern onto the sheet-contacting side of the fabric as described in U.S. Pat. No. 4,528,239 to Trokhan, EP 988,419 B1 to Huston, U.S. Pat. No. 6,398,910 B1 to Burazin and Chiu, or US patent application US 2006/0182936 A1 to Payne et al.
What is needed in the art is a papermaking fabric with improved runnability on the papermachine, for example, by improving vacuum operating windows, improving sheet adhesion to a Yankee dryer to improve creping and drying, reducing through air drying loads by eliminating pinholes, or improving fabric life through increased fabric robustness or reduced wear. What is also needed in the art is a papermaking fabric offering improved topography to allow increased tissue bulk.